1. Field of the Invention
The present invention relates to a washer pump mounted in, for example, an automobile and adapted to selectively supply wash fluid in a washer tank to both front and rear windows.
2. Description of the Prior Art
In the past, as such a type of washer pump above described, for example, there has been one as shown by FIGS. 9 and 10. Referring to FIGS. 9 and 10, the washer pump 101 has a motor chamber 111 enclosing a reversibly rotatable motor 102, a wash fluid suction pipe 112 communicating with a washer tank, not shown, a pump chamber 113 communicating with the suction pipe 112 and enclosing the impeller 103 fixed to the output shaft 102a of the motor 102, and a pump case 110 integrally provided with two wash fluid feed pipes 114A, 114B communicating with the pump chamber 113.
The pump case 110 is integrally provided with the motor chamber 111, the suction pipe 112, the pump chamber 113, the two feed pipes 114A, 114B, two wash fluid delivery pipes 115A, 115B communicating with the two feed pipes 114A, 114B respectively, and two valve seats 116A, 116B each located between the two feed pipes 114A, 114B and the two delivery pipes 115A, 115B and facing each other. Also, mounted between the two valve seats 116A, 116B is an elastic membrane 104 which divides the space between the two valve seats 116A, 116B into one side space where the valve seat 116A is located and the other side space where the valve seat 116B is located.
The washer pump 101 acts in such a manner that the rotation of the impeller 103 in one direction by the actuation of the motor 102 causes wash fluid to flow through the feed pipes 114A, 114B from the pump chamber 113 to one side space where the valve seat 116A is located and the other side space where the valve seat 116B is located respectively, with difference in pressure between wash fluid in the feed pipe 114A and wash fluid in the feed pipe 114B, and then one wash fluid passage is closed by the elastic membrane 104 at the valve seat 116A (or the valve seat 116B) on low pressure side of the two feed pipes 114A, 114B while the other wash fluid passage is opened at the valve seat 116B (or the valve seat 116A) on high pressure side of the two feed pipes 114A, 114B, so that wash fluid is delivered from the delivery pipe 115B (or the delivery pipe 115A) communicating with the space where the valve seat 116B (or the valve seat 116A) is located. As well, the above-mentioned prior arts are disclosed by Japanese Patent Publication No. 5-49840 and U.S. Pat. No. 4,600,361.
The conventional washer pump 101 as described above, however, is actuated in such a manner that the difference in pressure between the two feed pipes 114A, 114B causes the center portion of the elastic membrane 104 to move toward the valve seat 116A (or the valve seat 116B) on the side of low pressure feed pipe 114A (or 114B) against the elastic force of the elastic membrane 104 to close one wash fluid passage at the valve seat 116A (or 116B), so that one of the two delivery pipes 115A, 115B is selected so as to deliver wash fluid. Accordingly, the force for moving the center portion of the elastic membrane 104 toward the valve seat on the low pressure side and the force (or the sealing force) for keeping the wash fluid passage closed decrease by the elastic force of the elastic membrane 104, and the effective pressure area of the elastic membrane 104 decreases by the amount corresponding to the extension of the center portion thereof, and therefore the selection of the delivery pipe to be closed or opened, namely, the change-over of the delivery pipes 115A, 115B may not be performed completely, or may consume much time, and further leakage of wash fluid from the delivery pipe to be closed may occur, and furthermore when high viscous wash fluid is used, the washer pump is actuated at low temperatures, or the voltage in the battery supplying electric power to the motor 102 has dropped, the center portion of the elastic membrane 104 hardly moves in an axial direction. As a result, it becomes difficult to change over the delivery pipes 115A, 115B.
Further, in the conventional washer pump 101, because the pump case 110 is integrally formed with the motor chamber 111, the suction pipe 112, the pump chamber 113, two feed pipes 114A, 114B, two delivery pipes 115A, 115B communicating with two feed pipes 114A, 114B respectively, and two valve seats 116A, 116B located between two feed pipes 114A, 114B and two delivery pipes 115A, 115B and facing each other, the pump case 110 enlarges to limit the degree of freedom for setting itself.